The development of “green fuel” by using technologies for cleaning efficiently coal resources has important strategy meaning and use foreground from the point of resource utilization and environmental protection as China being largest coal-output country in the world.
The synthesis of hydrocarbons and oxygenates by catalytic hydrogenation of CO is one of the important approaches for clean utilization of coal resource. In recent year, the use value of lower carbon mixed alcohols in the field of fuel and chemical industry appears stepwise, and the related researches are active increasingly.
Homogeneous catalysts for synthesis of lower carbon mixed alcohols can be broadly grouped into two categories of noble metal and non noble metal, wherein noble metal Rh catalyst can convert syngas into ethanol and other oxygenates having two carbons or more. However, Rh metal is expensive due to the limited supply, thus the scale in commercial use thereof is limited. On the other hand, the main non noble metal catalysts for producing lower carbon mixed alcohols from syngas comprises modified methanol synthesis catalysts, modified Fischer-Tropsch (F-T) synthesis catalysts; and alkali metal-doped Mo catalysts. Among these catalysts, representative catalyst systems having industrial use foreground can be grouped into the following 4 categories:
(1) MoS catalyst system developed by Dow Chemical Company (Sygmol process);
(2) Cu—Co catalyst system developed by French Institute of Petroleum Institute (IFP process);
(3) Cu—Zn—Al catalyst system developed by Lurgi Company (Octamix process); and
(4) Zn—Cr—K catalyst system developed by Sham Company (MAS process).
In spite of the individual outstanding features of the above 4 catalyst systems, the developed catalysts have insufficiency in terms of activity, selectivity, stability, economy, and the like. The development of catalysts having high activity and high selectivity toward oxygenates having two carbons or more is still the difficulty and key point of the researches. Although the researchers had made a great deal of efforts on the development of these catalyst systems, there is still a very large space to improve the catalytic activity and selectivity toward higher alcohols.
Transition metal phosphides, being an important hydrogenation catalyst, show similar properties of noble metals in many reactions involving hydrogen and have the potential possibility for replacing noble metal catalysts. Kevin J. Smith et. al. (Appl. Catal., A 2010, 378, 59-68, Catal. Today 2011, 171, 266-274) studied the use of molybdenum phosphide catalyst in the hydrogenation reaction of CO, showing that the products thereof are significantly different with those in the case where conventional non-noble metal catalysts are used. The content of oxygenated products having two carbons or more in the liquid phase products reaches to 76% (C %).